I am sorry dgb, but I dont think that is possible. The aliases for the same account give the users same access rights to mail. For all intents and purposes, they are the same account.
Possible workaround.

I am sorry dgb, but I dont think that is possible. The aliases for the same account give the users same access rights to mail. For all intents and purposes, they are the same account.

Possible workaround. Send all the mail to a third account (like an administrative account). Set up a rule on the admin account (server side) so it splits up the mail based on aliased. Of course, the two users will still have to use other email accounts or internal only email accounts in order for that to work.

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This video shows how to remove a single email address from the Outlook 2010 Auto Suggestion memory.
NOTE: For Outlook 2016 and 2013 perform the exact same steps.
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Start typing the address: …